JP2008507150A - LED array package with internal feedback and control - Google Patents

Abstract

A packaged LED array for high temperature operation comprises a metal base that includes an underlying thermal connection pad. One or more ceramic layers are on the metal layer. The array includes a plurality of LED dies, each LED die having an electrode. The LED is also thermally coupled to the metal base. The driver circuit is electrically connected to the LED die electrode and controls the LED array current. The LED driver is mounted in the LED array package and is thermally coupled to the metal base. In a second embodiment, one or more of the LED dies can be switched from a driver to a measurement circuit and used as a photodetector to measure the light output of the LED array. The measured photodetector signal can further be used as a feedback signal to control the LED array light output.

Description

  The present invention relates to an apparatus for simultaneously packaging a light emitting diode (LED) array having an electronic driver and a feedback circuit, wherein the electronic driver and control circuit are incorporated within the LED array package. The present invention also relates to a method and apparatus for monitoring and controlling LED array light output using one or more dies of the LED array as a photodetector.

  Light emitting diodes (LEDs) are useful in a variety of applications. An LED array is an array of LED dies mounted on a common substrate. LED arrays are used as light sources in a wide variety of applications including communications and instrumentation, commercial and home room lighting, and automotive and visual displays. An LED array is a device comprising a plurality of LEDs on the same substrate. LED arrays can be made by various techniques.

  One problem with LED arrays is that considerable heat is generated by the close concentration of LEDs. A solution to the thermal problem associated with LED arrays is disclosed in a related application entitled “Light Emitting Diodes Packaged For High Temperature Operation”, US patent application Ser. No. 10 / 638,579, filed Aug. 11, 2003. The subject. Another issue related to LED array performance, lighting efficiency is the subject of a related application entitled “Efficient LED Array”, US patent application Ser. No. 10 / 822,191, filed Apr. 9, 2004. . Both of these two applications are hereby incorporated by reference.

  LED arrays have been successfully created using low temperature co-fired ceramics (LTCC-M) packaging technology on metal. The LTCC-M structure and materials are described in US Pat. No. 6,455,930, “Integrated Heat Sinking Packages Using Low Temperature Co-Fired Ceramic Circuit Board Technology, Monthly, Published 24th, 2002”. . The LTCC-M structure is further described in US Pat. Nos. 5,581,876 (issued on Dec. 10, 1996), 5,725,808 (issued on Mar. 30, 1998), and 5,953,203. (Issued on Sep. 14, 1999) and No. 6,518,502 (issued on Feb. 11, 2003). All of which are available at Lamina Ceramics Inc. US Pat. Nos. 6,455,930, 5,581,876, 5,725,808, 5,953,203, and 6,518, No. 502 is also incorporated herein by reference.

  In many applications, it is advantageous to control the LED array with an electronic driver circuit. The driver can turn the LED on or off, or control the output luminous intensity. An active power semiconductor can be used to provide the driver function. The driver control signal can be simply an on-off command, usually in the form of a low level control signal or a logic signal. Alternatively, the control signal can be an electrical signal that sets the current through the LED for the desired light intensity. When controlling the LED current to set the brightness of the LED array, it is further advantageous to include feedback and control circuitry. Photodetector components can be placed near the LED array to measure the light output and provide the required feedback signal. The problem is the cost and complexity of the additional detector and the mechanical structure required to mount the detector in or near the array.

It would be very advantageous to provide an LED array having a control circuit that includes a built-in electronic driver and a sensor for feedback control. Although such a circuit is necessary, it has been difficult to package on the same substrate as the LED. Typically, application specific LED drivers and control circuits are built on a printed wiring board (PCB) outside the LED array. This is a problem for applications that must be installed in a small space. LED arrays using external PCB mounted electronics are also expensive. Past attempts to incorporate driver circuitry into LED array packages have been largely successful due to mechanical stresses caused by differences in thermal expansion coefficients between the semiconductor die and prior art LED packaging methods and materials. It did not lead to.
US patent application Ser. No. 10 / 638,579 US patent application Ser. No. 10 / 822,191 US Pat. No. 6,455,930 US Pat. No. 5,581,876 US Pat. No. 5,725,808 US Pat. No. 5,953,203 US Pat. No. 6,518,502

  Accordingly, there is a need for an improved LED array device that can package drivers, control circuitry, and photodetector sensors simultaneously in an array without cost.

  The present invention provides a packaged LED array for high temperature operation. In one embodiment, the present invention provides a packaged LED array comprising a metal base that includes an underlying thermal connection pad. One or more ceramic layers are on the metal base. The array includes a plurality of LED dies thermally coupled to a metal base, each LED die having an electrode. To provide control of the LED array current, a driver circuit is mounted in the LED array package and electrically connected to the LED die electrode. Preferably, at least a portion of the driver circuit is thermally coupled to the metal base.

  In the second embodiment, one or more LED dies can be connected from the driver circuit to the measurement circuit and used as a photodetector to measure the light output of the LED array. Furthermore, the measured photodetector signal can be used as a feedback signal to control the LED array light output.

The advantages, features, and various additional features of the present invention will become more fully apparent upon consideration of the specific embodiments herein set forth in detail with reference to the accompanying drawings.
It should be understood that these drawings are for purposes of illustrating the concepts of the invention and do not follow a scale except for the graph.

  The detailed description consists of four parts. Chapter I discloses several embodiments of embedded feedback and control for use in LED array packages. Section II describes using one or more of the LED dies in the LED array to provide array feedback and control. Section III describes an LED driver circuit suitable for use with the present invention. Section IV describes LTCC-M packaging technology as it relates to the present invention.

Chapter I: LED Array with Integrated Feedback and Control Referring to the drawings, FIG. 1 shows an exemplary LED array 10. Seven cavities are formed in the ceramic circuit, and six LED dies 11 are attached to the metal base of each cavity. Electrical connections are made to the die through wire bonds 12 and through gold electrodes on a metal base.

  FIG. 2 shows a block diagram of an exemplary LED array package 100 that includes an LED array 10 that incorporates an embedded driver circuit 21, feedback 23, and detector 22. In one embodiment shown in FIG. 2, a pulse width modulator (PWM) 21 is used as a driver circuit. The LED array 10 can be driven by any driver circuit suitable for use in the present invention and described in more detail in Section III of this application. The driver circuit 21 may also include an error amplifier for closed loop feedback operation based on the measured parameter input. Such measured parameters can include, but are not limited to, array current, voltage, power, brightness, luminous flux, light color, magnetic field, or temperature. The desired feedback parameter can be measured by the detector 22 and provided to the driver circuit 21 by a signal on the feedback 23.

  Those skilled in the art understand that when measuring parameters such as current, the detector 22 can be connected in series with an array (shown) or a Hall effect type current sensor. For measurement of other parameters, the sensor can be located other than what is literally shown in the block diagram. For example, the array voltage is measured across the LED array terminals, and the light is detected by a photodetector in the visible proximity of the illumination generated by the array, as shown in the block diagram of FIG. Please understand that you can.

FIG. 3 illustrates one embodiment of a pulse width modulated driver with a circuit topology suitable for use with the embedded LED array 10. This exemplary circuit topology uses a semiconductor device that includes a PWM controller U1, a Zener diode CR1, and a power field effect (FET) transistor Q1. The semiconductors used in the present invention are readily available commercially in die form for direct integration in packages such as LED arrays. For example, semiconductors for use in the present invention are available from Fairchild Semiconductor (McLean, VA), Microsemi Corporation (Urban, CA), Motorola, Inc. (Schaumburg, Ill.), International Rectifier (El Segundo, CA), and National Semiconductor (Santa Clara, CA).
(“Fairchild Semiconductor”, “Microsemi”, “Motorola”, “International Rectifier”, and “National Semiconductor” are company names or trademarks, respectively.)

  Most of these devices have a temperature coefficient on the order of 5 ppm / degree C, which is poorly matched to prior art LED array substrates having a coefficient of thermal expansion of 15-20 ppm / degree C. Due to these mismatches, the semiconductor can be subjected to very large mechanical forces due to the heating caused by the LED array. These forces can cause cracks and ruptures in the device that can cause initial LED array failure. Faults include from intermittent or reduced light output to destructive faults where there is no array light output.

  In one embodiment of the invention, this problem is solved by mechanically bonding the die to a glass layer having the same coefficient of thermal expansion and mounting such a device on a layer of an LTCC-M packaged array. As a result, mechanical forces are significantly reduced and more typical semiconductor lifetimes and failure rates can be achieved. The LTCC-M technology is described in more detail in section IV of this application.

  In another embodiment of the present invention, improved thermal management can be achieved by creating LED arrays with LTCC-M technology with integrated drivers and / or control loops containing drivers. The LED die and driver and other loop electronics all generate significant heat that travels from the LED die and other chips. Heat removal is necessary to prevent excessive temperature rise of the electronic devices embedded in the array and array package. By mounting these devices on or in the glass layer and / or metal substrate, excellent passive cooling can be achieved. For electronic circuits embedded in a glass layer, conductive and non-conductive thermal vias can further increase the waste heat flow by flowing the waste heat flow through the metal substrate.

  FIG. 5 shows an LED array package 50 that includes an LED array 52 having a driver circuit 51 incorporated within the LED array package 50. Additional openings and circuit interconnections in the ceramic circuit may be created to accommodate the attached driver circuit 53 such as the SMT capacitor shown in FIG. It is preferable to mount the driver circuit 51 in the cavity 54. In this embodiment, the driver 51, feedback and control, and the criteria for setting the LED light output can be mounted in the cavity 54. Preferably, power is provided to LED array 52 via contact pads 55,56. The contact pads 55, 56 can be made from any commercially available material, providing a reliable high current power connection. Contact pads 55, 56 can be constructed of any suitable weldable material including, but not limited to, silver, copper, nickel, or tin-lead. In a preferred embodiment, the contact pads 55, 56 are made of silver palladium.

  As shown in the block diagram of FIG. 6, a photodiode light output detector 61 may be used to detect light emitted from the LED array 10. Suitable commercially available photodiode light output detectors for use with the present invention include, but are not limited to, Vishay Intertechnology, Inc. (Including “Vishay Intertechnology” is a company name or trademark, and “Vishay BPW21R” is a trade name or a trademark). If the light output from the array decreases with time, temperature, age, or changing driver parameters, the output of detector 61 will drop accordingly. Thus, the resulting feedback to the LED array driver 62 will increase the output of the driver 62 and thus maintain the desired output of the LED array 10.

  In yet another embodiment, additional terminals are provided that allow a user to remotely control the LED array by providing a control reference input signal. In general, control refers to controlling all of the elements of the array at the same time, but there may be a form of independently controlling a cluster of LED dies 11 or individual LED dies 11. Typically, the input control reference signal is an analog control signal, but can also be a digital control signal, in which case the LED array further comprises a digital circuit suitable for receiving the digital control signal. Directly control the driver circuit, provide a reference to digitally controlled internal feedback and control loops, or convert to analog control signals on the LED array assembly as with a digital-to-analog converter Thus, the digital signal can control the LED array. Alternatively, pseudo-digital control can be achieved by a frequency-to-analog signal converter built in the LED array.

Chapter II: Using an LED Array as a Detector of One or More LEDs In another embodiment, one or more of the LED dies of the LED array can be switched from a driver circuit to a light measurement circuit to It can be used as a photodetector for measuring the light output. According to one embodiment shown in FIG. 7, the output light from the LED array 10 is detected by using one or more of the LED dies in the LED array 10 as a photodetector (see FIG. 7). ). In operation, one or more LED dies of the LED array 10 are alternately electrically connected by a switch 71 to the driver circuit 62 or the light measurement circuit 80 and the feedback 64. The LED die 11 functions as a light source when connected to the driver circuit 62, and functions as a photodetector 63 when periodically and temporarily disconnected from the driver circuit 62 by the operation of the switch 71.

  According to one embodiment, FIG. 7 shows LED array 10 with switch 71 in a position such that the farthest left LED die of LED array 10 operates as LED photodetector 63. By being disconnected from the driver circuit 62, the photodetector 61 detects light emitted from the adjacent LEDs 11A and 11B. Using this technique, the array light output can be periodically sampled by measurement circuit 80 and fed back to driver circuit 62 via feedback 64.

  Therefore, the driver circuit 62 can make an appropriate adjustment in the control of the LED array 10 according to the measurement value provided by the measurement circuit 80. When the measurement of the light output of the LED array 10 is completed, the measurement circuit 80 operates the switch 71 (control during operation indicated by a broken line in FIG. 7) to reconnect the photodetector 61 to the driver circuit 62. .

  One or more LED dies connected to the switch 71 used for the photodetector can be switched quickly from the detection mode to the original light emission mode, preferably in less than 10 ms. At this relatively fast switching rate, the light observer will not perceive the light detection sampling mode. Using one or more LED dies of the LED array 10 for the photodetector reduces the cost and complexity of the device compared to using an independent photodetector.

  Applications using one or more LED dies of the LED array 10 as photodetectors include, but are not limited to, output light adjustment and LED failure detection. In the light conditioning function, the LED die operating as a photodetector is useful as a linear feedback element for feedback and control circuits, as detailed in Section I. In the case of fault detection, the photodetector 63 can detect a threshold change in power level indicative of low light emission from one or more emitters of the LED array. This detection mode is advantageous compared to the electrical detection method. For example, one drawback of electrical detection schemes is that low light output can only be estimated by detecting changes in parameters such as LED current.

Specific Example The following is an example of a device comprising a light emitting diode array that is packaged simultaneously, where one or more of the LEDs are used as a photodetector to detect the light output of the LED array. The device is constructed starting from a suitable metal laminate base. It is preferred to use a 13% copper, 74% molybdenum, 13% copper (CMC) metal laminate. More preferably, H.M. C. CMC metal laminates manufactured by Stark Corporation (Newton, Mass.) Can be used in accordance with the present invention (“HC Starck” is a company name or trademark).

  Thick film gold bonding pads corresponding to the location of each die can be fired on the metal base to include the LED die, and any die can be used for control and feedback. The pad can be electrically and thermally connected to the CMC base. CMC compatible ceramic tape layers can be used to form die cavities, make electrical connections, and form array housings. Ceramic tapes are composed of commercially readily available glass and resin, including but not limited to those supplied by Ferro Corporation (Cleveland, Ohio), etc. (where “Ferro” is a company name or trademark) .) The tape material can be crushed, mixed and cast into a flat sheet. The sheet can then be processed using typical “green” tape processing including punching, printing, collating, and pasting. These techniques are well known to those skilled in the art. The CMC base is attached during lamination and joined to the tape layer during ˜900 ° C. firing. Multiple arrays can be processed on a single wafer and then cut and separated by dicing after firing.

  After the base module is provided in the ceramic layer, the individual dies are preferably connected by soldering to the gold pads in the bottom of each cavity using 80% Au / 20% Sn solder. Alternatively, each die can be connected to a gold pad using conductive epoxy, including but not limited to Ablebond 84LM1, commercially available from Emerson & Cuming (Canton, Massachusetts). , And “Ablebond84LM1” are trade names or trademarks).

  A gold pad can be connected to the metal base. Conductive vias are used to connect the electrical terminals on the top ceramic layer to the metal base. The anode or cathode can be commonly connected to the back of the die, and then the back is connected to a gold bonding pad. Wire bonds can be used to electrically connect the opposing faces of the die to the array. Bonds can be connected from the die to bonding pads on one of the ceramic layers. Also, pressure film conductive traces can be deposited on the surface of the ceramic layer including the bonding pads. The traces can be connected to electrical terminals on the top ceramic layer through conductive vias. Various die connections are possible, including series, parallel, and series-parallel combinations.

  According to a specific example, a package with seven cavities is produced. Each cavity includes three red LEDs, three green LEDs, and one blue LED. When power is applied to a single color of the LED array, the light output of the other LED can be detected by measuring the voltage developed across one LED of the other color LEDs.

  The light output from a particular color LED is preferably detected using another LED with the same or longer wavelength emission. For example, in order to detect the output of a green LED (505 nm wavelength), it is preferable to use a red LED (625 nm wavelength) superimposed on a blue LED (470 nm wavelength). Furthermore, it is contemplated that one or more of the red LEDs can be used to detect the output of the remaining red LEDs in the array. The light sensitivity of an LED is another factor to consider when determining the appropriate LED to use as a detector.

  More preferably, different detector LEDs should be used in their most efficient detection range. The detection range should be selected so that the detector operates just below the curve break shown in FIG.

  In addition, resistors, inductors and capacitors that drop voltage and limit current are added as components that are embedded in the middle of the ceramic layer or as separate components that are mounted on the top surface of the package can do. Additional control, ESD protection, and voltage regulation semiconductors may be added in die or packaged form. Finally, a refractive index matching epoxy, such as Hysol® 1600, available from Henkel Loctite® Corporation (Troutbrook Crossing, Rocky Hill, Conn. 1001) is applied to each die cavity to protect the device. Can be added.

Chapter III: LED Drivers for Use with the Present Invention Some LED array light characteristics may be corrected using automatic control. For example, the light output (flux or radiant flux) may be controlled by including a constant current driver in the LED array. The light output (φ) of the LED over its linear operating range is proportional to the forward DC current,
φ = ηIV
Given by. here,
η is the diode external quantum efficiency,
I is the forward diode current, and
V is the forward diode voltage.

  FIG. 8 shows an example of an LED driver suitable for use with the present invention. A silicon bipolar transistor shown in FIG. 8 may be used to keep the diode current constant. FIG. 9 shows another constant current driver suitable for use with the present invention. The driver includes a current mirror that drives a plurality of diode strings having the same forward current. Another option for constant current operation is a dedicated integration specifically designed for this purpose, such as the LM134 3-terminal adjustable current source available from National Semiconductor Corporation (Santa Clara, Calif.) As shown in FIG. Circuit (the “National Semiconductor” is a company name or a trademark). FIG. 10 illustrates an exemplary multiple string constant current driver circuit suitable for use with the present invention.

  The circuits shown in FIGS. 8, 9, and 10 are advantageously simple and inexpensive drivers for use with the present invention. Yet another driver circuit for use with the present invention is the variable pulse width control (VPWC) circuit shown in FIGS.

  Referring to FIG. 2, the PWM circuit 21 can change the current or voltage pulse width based on the feedback signal from the parameter detector 22. The detector 22 can be used to monitor power consumption, current, voltage, temperature, luminous flux or radiant flux, or other desired parameters. The PWM output can serve to produce the desired feedback regardless of load (LED array 10) changes or input variations.

  The circuit shown in FIG. 3 controls the power delivered to the LED array 10 for a wide range of input voltages. This circuit is useful in automotive applications where the input voltage can vary from a low level during battery operation to a high level during battery charging. This circuit is designed to maintain constant power for the LED (s) connected across C3 for input voltage (VCC) variations of 9-20 volts. Constant power (constant light output) is maintained by changing the current pulse width for the LED (s). As the input voltage increases, the pulse width becomes narrower. Pulse width variation helps to minimize power consumption. Circuits with efficiencies greater than 90% are common.

  According to another embodiment, the circuits shown in FIGS. 2, 3, 6, 7, 8, 9 and 10 are described in detail in Section IV and in the exemplary LTCC-M array shown in FIG. Can be built.

Chapter IV: LTCC-M Packaging LTCC-M packaging is particularly suitable for LED arrays due to the high heat generated by a closely packaged array of LED dies. This section highlights some of the important aspects of LTCC-M packaging as applicable to making LED arrays with reflective barriers.

  Multilayer ceramic circuit boards are made from layers of green ceramic tape. Green tapes are made from specific glass components and optional ceramic powders, which are mixed with an organic binder and solvent, cast and cut to form the tape. A wiring pattern can be screen printed on the tape layer to perform various functions. Thereafter, vias are drilled into the tape, filled with conductive ink, and the wiring on one green tape is connected to the wiring on another green tape. Thereafter, the tape is aligned, laminated and fired, the organic material is removed, the metal pattern is sintered, and the glass is crystallized. This is generally performed at a temperature of less than about 1000 degrees C., preferably about 750 to 950 degrees C. The composition of the glass determines the coefficient of thermal expansion, the dielectric constant, and the suitability of the multilayer ceramic circuit board for various electronic components. Exemplary crystallization glasses with inorganic fillers that sinter in the temperature range of 700-1000 degrees C. are magnesium aluminosilicate, calcium borosilicate, lead borosilicate, and calcium aluminoborate.

  Until very recently, metal support substrates (metal plates) have been used to support green tape. The metal plate gives strength to the glass layer. Because the green tape layer can be mounted on both sides of the metal plate and can be secured to the metal plate with a suitable bonded glass, the metal plate allows for increased circuit and device complexity and density. In addition, passive and active components such as resistors, inductors, and capacitors can be incorporated into the circuit board for additional functionality. When installing optical components such as LEDs, the walls of the ceramic layer can be shaped and / or coated to enhance the reflective optical properties of the package. Alternatively, a reflective barrier can be used to further improve both the illumination efficiency and thermal efficiency of the LED array package.

  This system, known as low temperature co-fired ceramic on metal support plates or LTCC-M, has been found to be a means of highly integrating various devices and circuits in a single package. The system is adjusted to be compatible with devices including, for example, silicon-based devices, indium phosphide-based devices, and gallium arsenide-based devices by appropriate selection of metal for the support plate and glass in green tape. be able to.

  The ceramic layer of LTCC-M structure must match the coefficient of thermal expansion of the metal support plate. Glass ceramic components are known that match the thermal expansion properties of various metals or metal matrix composites. Although the metal support plates used in LTCC-M technology show high thermal conductivity, some metal plates have a high coefficient of thermal expansion, so it is always possible to mount the bare die directly on such metal support plates. It's not possible. However, copper and molybdenum made using powder metallurgy techniques (including copper percentages of about 10% to about 25% molybdenum) or copper and tungsten (copper weight) can be used for these purposes. Some metal support plates are known, such as metal composites (including a percentage of tungsten of about 10% to about 25%). AlSiC is another material that can be used for direct attachment, as can aluminum or copper graphite composites. An example of a suitable support plate for use in the present invention is Copper clad Kovar®, which includes iron, nickel, cobalt, and Manganese metal alloys. Copper clad Kovar (R) is a product of Carpenter Technology (Leading Pennsylvania) ("Carpenter Technology" is a company name or trademark).

  Another application that requires efficient cooling requires thermal management of flip chip packaging. Devices such as closely packaged microelectronic circuits and decoder / drivers, amplifiers, oscillators, etc. that generate large amounts of heat can also advantageously use LTCC-M techniques. Metallization on the top layer of the integrated circuit provides input / output lines at the edge of the chip so that it can be wire bonded to the package or module containing the chip. Therefore, the wire length of the wire bond becomes a problem, and a wire that is too long causes a parasitic component. The cost of very high integration chips may be determined by bond pad layout rather than by the silicon area required to make the circuit. Flip chip packaging overcomes at least some of these problems by using solder bumps rather than wire bond pads to make connections. These solder bumps are smaller than the wire bond pads and solder reflow can be used to attach the chip to the package when the chip is turned upside down, i.e. flipped over. Due to the small solder bumps, when using multi-layer packaging, the chip can include input / output connections therein. Thus, the number of dies in a chip, not the number and size of bond pads, will determine the chip size.

  The ceramic layer of LTCC-M structure must match the coefficient of thermal expansion of the metal support plate. Glass ceramic components are known that match the thermal expansion properties of various metals or metal matrix composites. The LTCC-M structure and materials are disclosed in US Pat. No. 6,455,930 issued to Ponwaswamy et al. On September 24, 2002 and assigned to Lamina Ceramics, “Integrated Heat Sinking Packages Using Low Temperature Co-. fired Ceramic Metal Circuit Board Technology ". US Pat. No. 6,455,930 is hereby incorporated by reference. The LTCC-M structure is further described in US Pat. Nos. 5,581,876, 5,725,808, 5,953,203, and 6,518,502, all of which Assigned to Lamina Ceramics and similarly incorporated herein by reference.

  Although metal support plates used in LTCC-M technology have high thermal conductivity, some metal plates have a high coefficient of thermal expansion, so that the bare die should always be mounted directly on such metal support plates. Is not possible. However, copper and molybdenum (including about 10-25% copper weight) or copper and tungsten (about 10-25% copper weight) made using powder metallurgy techniques can be used for these purposes. Some metal support plates are known, such as metal composites. Copper clad Kovar (registered trademark of Carpenter Technology), which is a metal alloy of iron, nickel, cobalt, and manganese, is a very useful support plate. AlSiC is another material that can be used for direct attachment, as can aluminum or copper graphite composites.

  Thermal management of flip chip packaging is yet another application that requires efficient cooling. Devices such as closely packaged microelectronic circuits and decoder / drivers, amplifiers, oscillators, etc. that generate large amounts of heat can also advantageously use LTCC-M techniques. Metallization on the top layer of the integrated circuit provides input / output lines at the edge of the chip so that it can be wire bonded to the package or module containing the chip. Therefore, the wire length of the wire bond becomes a problem, and a wire that is too long causes a parasitic component. The cost of a very integrated chip may be determined by bond pad placement, not by the silicon area required to make the circuit. Flip chip packaging overcomes at least some of these problems by using solder bumps rather than wire bond pads to make connections. These solder bumps are smaller than the wire bond pads and solder reflow can be used to attach the chip to the package when the chip is turned upside down, i.e. flipped over. Due to the small solder bumps, when multi-layer packaging is used, the chip can include input / output connections therein. Thus, the number of dies in a chip, not the number and size of bond pads, will determine the chip size.

  However, increasing the density and integration of functions on a single chip can increase the temperature on the chip and prevent full utilization of the optimum circuit density. The only heat sink is a small solder bump that connects the chip to the package. If this is insufficient, a small active or passive heat sink must be added on top of the flip chip. Such additional heat sinks increase assembly costs, increase the number of parts required, and increase package costs. In particular, heat sinks also have limited efficiency if they have a small heat volume.

  In the simplest form of the invention, LTCC-M technology is used to provide an integrated package for semiconductor components and associated circuitry, and a conductive metal support plate provides a heat sink for the components. For example, a semiconductor bare die can be mounted directly on the metal base of an LTCC-M system with high thermal conductivity to cool the semiconductor components. In such cases, the electrical signal that operates the component must be connected from the ceramic to the component.

  Indirect attachment to a metal support plate can also be used. In this package, all the required components are thermally coupled to a metal support plate that can also incorporate embedded passive components such as conductors and resistors in a multilayer ceramic part, and various components, i.e. Semiconductor components, circuits, heat sinks, etc. are connected in an integrated package. For LED arrays where electrical circuit issues dictate the use of insulating materials, heat conduction can be a problem. In this case, the reflective barrier further operates as a thermal diffusion device that assists in the transfer of heat received by conduction and radiation through the insulating layer to the metal base.

  It is also possible to mount the LTCC-M circuit with a metal substrate surface on a printed wiring board or other patterned conductor mounting device. A pattern is cut into the metal substrate and the insulator defines an insulated electrical terminal within the metal substrate surface. These terminals are available from Lamina Ceramics, Inc. U.S. Pat. No. 6,518,502 (issued Feb. 11, 2003) to Hammond et al. US Pat. No. 6,518,502 is incorporated herein by reference.

  For more complex structures with improved heat dissipation, the integrated package of the present invention combines first and second LTCC-M substrates. The first substrate can be mounted with a multilayer ceramic circuit board having embedded circuits for operating semiconductor devices and components, and the second substrate is mounted with a heat sink or a conductive heat spreader. A thermoelectric (TEC) plate (Peltier device) and a temperature control circuit are mounted between the first substrate and the second substrate to provide improved temperature control of the semiconductor device. The hermetic containment vessel can be secured to the metal support plate.

  Through the use of LTCC-M technology, the benefits of flip chip packaging can be exploited along with heat dissipation integration. The package of the present invention can be made smaller, cheaper and more efficient than existing current packaging. The metal substrate operates as a heat spreader or heat sink. The flip chip can be mounted directly on the metal substrate that is an integral part of the package, eliminating the need to add a heat sink. A flexible circuit can be mounted on the bumps on the flip chip. The use of multilayer ceramic layers can also achieve trace fanout and routing to the package perimeter, further improving heat dissipation. High power integrated circuits and devices with high thermal management needs can be used with this new LTCC-M technology.

  FIG. 4 shows a cross section of an exemplary LED array package using the LTCC-M configuration. The LTCC-M structure consists of a thermally conductive metal base connected to a multilayer ceramic circuit board 42. An opening 43 in the ceramic circuit board 42 is made to accommodate the semiconductor die 44 and other components. The components are attached directly to the metal base 45. The metal base 45 can be composed of any suitable material such as copper tungsten, Kovar, or a metal laminate such as copper molybdenum having various thickness ratios. The metal base 45 is preferably made from copper cladding molybdenum. Attachment to the metal base 45 keeps the semiconductor die 44 cool, enabling efficient and reliable operation.

  Typically, connections to the semiconductor die 44 are made using wire bonds 46 or by flip chip attachment (not shown). A polymer encapsulation 47 is preferably used to protect the wire bond 46.

  It is understood that the above-described embodiments represent only a few of the many possible specific embodiments that can show the application of the present invention. Numerous and varied other arrangements can be made by those skilled in the art without departing from the spirit and scope of the invention.

FIG. 3 illustrates an exemplary LED array. FIG. 5 shows a block diagram of an LED array that incorporates an integrated driver, feedback, and control system. 1 is a schematic diagram of one embodiment of a pulse width modulated LED array control circuit. FIG. 3 is a cross-sectional view of an exemplary LTCC-M LED array. FIG. 3 is a block diagram of an exemplary LED array having integrated driver circuitry. It is a figure which shows the LED array which has an integrated type photodetector. FIG. 2 illustrates an exemplary LED array with an integrated photodetector, where one LED die of the array operates alternately as a photodetector and a light source. 1 is a schematic diagram of a transistor constant current driver circuit. 1 is a schematic diagram of an exemplary LM134 driver integrated circuit. 1 is a schematic diagram of a multiple string constant current driver circuit. It is a graph which shows the light beam detected using an LED die as a photodetector.

Claims (23)

An LED array package for high temperature operation,
A metal base,
A thermal connection pad under the metal base;
One or more ceramic layers overlying the metal base;
A plurality of LED dies including electrodes thermally coupled to the thermal connection pads through the metal base;
A LED array package comprising a driver circuit mounted in the LED array package and electrically connected to the LED die electrode.   The LED array package of claim 1, wherein at least a portion of the driver circuit is thermally coupled to the metal base.   The LED array package of claim 1, further comprising a cavity, wherein the plurality of LED dies are interconnected to form at least one LED cluster secured within the cavity.   4. The LED array package of claim 3, wherein the driver circuit controls the at least one LED cluster.   The LED array package of claim 1, wherein the driver circuit provides a plurality of independent outputs, and the LED dies are individually connected to and controlled by the independent outputs.   The one or more ceramic layers include thermally conductive vias to the metal base, and the driver circuit is mounted on the one or more ceramic layers and is thermally coupled to the metal base by the thermally conductive vias. The LED array package of claim 1, coupled to the LED array package.   The LED array package of claim 1, wherein the one or more ceramic layers further comprise conductive traces.   The LED array package of claim 1, wherein the one or more ceramic layers comprise printed circuit layers.   The LED array package of claim 1, wherein the driver circuit comprises a pulse width modulator or a linear current driver.   The LED array package of claim 1, wherein at least a portion of the LED die and the driver circuit are mounted on the outermost side of the one or more ceramic layers.   The LED array package according to claim 1, wherein at least a part of the driver circuit is mounted between the two ceramic layers.   The LED array package according to claim 1, wherein the package is an LTCC-M package.   The LED array package of claim 1, further comprising a feedback and control loop for adjusting the driver circuit to control LED parameters.   14. The LED array package of claim 13, wherein the LED parameter is selected from the group of parameters consisting of luminous intensity, luminous flux, array current, die current, voltage, magnetic field, temperature, brightness, and light source color. An LED array package for high temperature operation,
A metal base,
A thermal connection pad under the metal base;
One or more ceramic layers overlying the metal base;
A plurality of LED dies each having a pair of electrodes, wherein the LED dies are thermally coupled to the thermal connection pads through the metal base;
A driver circuit mounted in the package and thermally coupled to the metal base, the driver circuit having an output for controlling a current supplied to the LED die;
A measurement circuit for measuring the light output of the LED array;
And an electronic switch that switches connection of one or more LED dies from the driver circuit to the measurement circuit, and the one or more LED dies are disconnected when the one or more LED dies are disconnected from the driver circuit. The LED die operates as an LED photodetector, detects the light output of the LED array, generates a measured signal, and provides the measured signal to the measurement circuit;
An LED array package comprising a control circuit that receives the measured signal from the measurement circuit and controls the LED array light output by adjusting the driver circuit output.   The LED array package of claim 15, wherein the measured signal is a voltage or current of the LED photodetector.   16. The LED array package of claim 15, wherein the electronic switch connects the one or more LED dies to the measurement circuit for a period of ≦ 10 ms.   The LED array package of claim 15, wherein the package is an LTCC-M package.   The LED array package of claim 15, wherein the one or more ceramic layers further comprise conductive traces.   The LED array package of claim 15, wherein the one or more ceramic layers comprise printed circuit layers. A method of providing optical feedback in an LED array comprising:
Providing an LED array including a plurality of LED dies, driver circuits, and detector circuits;
Providing a switch for switching one or more of the LED dies from the driver circuit to the detector circuit;
Switching between the driver circuit and the detector circuit;
Measuring the light output of the LED array to provide a measurement signal using one or more of the switched LED dies;
Feeding back the measurement signal to the driver circuit to control the LED array light output.   The method of claim 21, wherein the step of switching includes switching between the driver circuit and the detector circuit at a rate fast enough to appear to be stable illumination for a person.   The method of claim 21, wherein the switching step includes switching the driver circuit and the detector circuit at a periodic rate.

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